Surface acoustic wave device

ABSTRACT

To obtain a surface acoustic wave device which can be produced with ease at a low cost and can be reduced in size without causing deterioration of characteristics, a surface acoustic wave device having input and output transducers arranged alternately on the surface of a substrate for propagating a surface acoustic wave includes metal patterns provided outside the transducers along the extension line of the propagation path of the surface acoustic wave and having at least one surface inclined at an angle θ (5°&lt;θ&lt;85° or -85°&lt;θ&lt;-5°) with respect to the propagation direction of the surface acoustic wave.

This is a continuation of application Ser. No. 08/468,559, filed Jun. 6,1995, which is a divisional of application Ser. No. 08/241,995, filedMay 12, 1994, now U.S. Pat. No. 5,485,051, which in turn is a divisionalof application Ser. No. 08/112,474, filed Aug. 27, 1993, now U.S. Pat.No. 5,396,199.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device, and,more specifically, to a surface acoustic wave device having low loss andfew ripples in in-band frequency characteristics.

2. Description of the Prior Art

In the conventional method for making an excellent surface acoustic wavedevice having low loss and excellent out-band frequency characteristics,patterns made of a metal thin film are formed outside input and outputtransducers and grounded. Such a method is disclosed, for example, inCPM 81-20 of Vol. 81 No. 78 of Denshi Buhin and Zairyo (electronic partsand materials), a technical research report issued by the Institute ofElectronics and Communication Engineers of Japan on Jul. 20, 1981. Theconfiguration of this type of surface acoustic wave device will bedescribed as a prior art corresponding to the first invention withreference to FIG. 3. FIG. 3 is a schematic diagram of this prior artcomprising three electrodes, which was drawn with reference to aphotograph included in the above-described document. In FIG. 3, thesurface acoustic wave filter of this prior art is structured such thattwo input transducers 2 and one output transducer 3 are arrangedalternately on a substrate 1 for propagating a surface acoustic wavealong the propagating direction of the surface acoustic wave, the inputtransducers 2 are connected to an input terminal 4 while the outputtransducer 3 is connected to an output terminal 5, and metal patterns 6which are grounded are arranged outside the input transducers 2. Todescribe the prior art briefly, the number of electrodes and the numberof electrode fingers are reduced to explain the basic structure of thedevice and the role of the metal patterns 6 outside the transducers isthe same as that of the prior art.

FIG. 5 is a schematic diagram of a surface acoustic wave deviceproposed, for example, in Utility Model Application No. 2-28125. In thefigure, reference numeral 1 represents a parallelogrammic substrate forpropagating a surface acoustic wave. On the substrate, two inputtransducers 2 and one output transducer 3 are arranged alternately alongthe propagating direction of the surface acoustic wave and the inputtransducers 2 are connected to the input terminal 4 while the outputtransducer 3 is connected to the output terminal 5.

A description is subsequently given of the operation of theabove-described prior art.

Electric power of an input signal supplied to the input terminal 4 isdivided by two and supplied to the input transducers 2 which convert theelectric power into a surface acoustic wave. The converted surfaceacoustic wave propagates toward both sides of the input transducers 2 asshown by the arrows of FIG. 3 or FIG. 5. The output transducer 3receives the surface acoustic wave and converts it into an electricsignal. The converted electric signal is then output from the outputterminal 5 as an output electric signal.

The surface acoustic wave propagating toward both end portions of thesubstrate 1 from the input transducers 2 is not received by the outputtransducer 3. Thereby, half of the total electric power being directedtoward both ends of the substrate 1 for propagating the surface acousticwave is discarded.

Generally speaking, when, at both end portions of the substrate 1 alongthe extension line of the propagation path of a surface acoustic wave,the surface acoustic wave leaked toward both end portions of thesubstrate 1 propagates from the input transducers constructed by metalpatterns toward both end portions of the substrate 1 where the metalpatterns do not exist, reflection is caused by mismatching of acousticimpedance due to the existence and non-existence of the metal patterns,leading to such deterioration of characteristics as ripples in amplitudecharacteristics and phase characteristics.

To overcome this problem, as shown in FIG. 3, metal patterns 6 areformed along the extension line of the propagation path of the surfaceacoustic wave. Then, mismatching of acoustic impedance is minimal orrarely occurs, thus causing little reflection, whereby the effect ofreflection at both end portions of the substrate 1 of the surfaceacoustic wave leaked toward both end portions of the substrate 1 can beminimized.

Meanwhile, a surface acoustic wave device which makes use of irregularreflection at both end portions of the substrate 1 is shown in FIG. 5.

FIG. 27 is a plan view of a surface acoustic wave device of a prior artcorresponding to the second invention as disclosed, for example, inJapanese Laid-Open Patent No. 1-292908. FIG. 28 is also a plan view of asurface acoustic wave device provided with grating reflectors of anotherprior art as disclosed, for example, in Japanese Laid-Open Patent No.62-12206. FIG. 29 is also a plan view of a surface acoustic wave deviceprovided with a multi-strip coupler of another prior art as disclosed,for example, in Japanese Laid-Open Patent No. 62-31212.

A description is given of the construction of each of the above priorarts. Reference numeral 2 and 3 represent input and output inter-digitaltransducers (hereinafter abbreviated as IDT) for converting an electricsignal into a surface acoustic wave or a surface acoustic wave into anelectric signal, respectively. Reference numeral 7 represents gratingreflectors for reflecting a surface acoustic wave, and 8 designates amulti-strip coupler (hereinafter abbreviated as MSC). Components 2, 3, 7and 8 are arranged on the surface of the substrate 1.

The input and output IDTs are constructed by electrode fingers 2a and 2band electrode fingers 3a and 3b, respectively, whose comb portions meshwith each other. The grating reflectors and the MSC are constructed by aplurality of strip lines.

Electron beam lithography may be used for patterning of the surfaceacoustic wave devices of these prior arts. In the electron beamlithography, an electron beam is irradiated onto a photosensitive agentfor exposure unlike photolithography in which a photomask pattern istransferred by light. This electron beam lithography is very effectiveespecially for the formation of fine patterns because of the shortwavelength of a radiation source.

Electron beam exposure is applied in the production of a photomask usedin the patterning of the above-described photolithography. The patternconfiguration of a photomask is exactly the same as that of a surfaceacoustic wave device.

However, since the prior art surface acoustic wave device correspondingto the first invention is structured as described above, in theconfiguration of FIG. 3, the surface acoustic wave leaked from endportions of the input transducers 2 is hardly reflected at theboundaries of the metal pattern 6 and the input transducer 2. However,when the surface acoustic wave propagates from an end portion of themetal pattern 6 toward an end portion of the substrate 1, it isreflected at an end portion of the metal pattern 6 due to mismatching ofacoustic impedance caused by the existence and non-existence of themetal pattern. This is based on the fact that the effect of reflectionof the surface acoustic wave propagating from the input transducers 2 atthe boundaries of the metal pattern 6 and the input transducer 2 can bereduced by adjusting the space between the input transducer 2 and themetal pattern 6, whereas it is difficult to control the effect at theboundaries of the metal pattern 6 and an end portion of the substrate 1.A surface acoustic wave device having 13 input and output transducersarranged alternately on the surface of a 64° Y-rotation, X-propagationlithium niobate substrate like the above-described prior art wasactually produced and it was found that the device was greatly affectedby reflection, as shown in FIG. 4. The term, a 64° Y-rotation,X-propagation lithium niobate substrate used herein, refers to asubstrate over the surface of which a surface acoustic wave propagatesand the plate normal of the surface of which is inclined at an angle ofmore than 59° and less than 69° from the Y axis of the crystalline axistoward the Z axis, and wherein the propagation direction of the surfaceacoustic wave forms an angle of more than -5° and less than +5° or morethan 175° and less than 185° with respect to the X axis of thecrystalline axis. This substrate has good performance in propagating asurface acoustic wave.

FIGS. 4, 6, and 7 show frequency response characteristics in the passband for prior art SAW filters. These are depicted in terms of loss as afunction of frequency in the pass band. As shown on the vertical axis,loss decreases toward zero in the upward direction. The response of theprior art devices shows the presence of ripples in the frequencyresponse characteristics in the pass band.

T1 of FIG. 4 represents a feedthrough signal (direct wave), t2 a mainsignal, t3 and t4 reflections from the metal pattern 6 of FIG. 3, and t5reflection from an end portion of the substrate 1. Frequencycharacteristics resulting from these signals are shown in FIG. 6.Frequency characteristics obtained from the configuration of FIG. 5 areshown in FIG. 7. A number of ripples, although small, remain in bothfrequency characteristics.

The configuration of the prior art device shown in FIG. 5 in which thesubstrate 1 becomes bulky is not suitable to reduce the size of thedevice.

The first invention is intended to solve the above problems and it is anobject of the present invention to provide a surface acoustic wavedevice which has a simple structure that can be constructed by the samemethod as that used for input or output transducers, can preventdeterioration of frequency characteristics caused by reflections of asurface acoustic wave leaked from both ends of the transducers, and canbe made small in size.

Since a conventional surface acoustic wave device corresponding to thesecond invention is structured as described above, in the case ofpatterning by means of the electron beam lithography, electronsirradiated from a radiation source onto a certain point of aphotosensitive agent move in the agent and affect other parts of thephotosensitive agent surrounding the point. As a result, photosensitiveconditions may differ at each part of the agent and variations in linewidth called "proximity effect" may occur.

In other words, as shown in FIG. 30, root portions 2e and 3e of theelectrode fingers may be thinner or partly broken, or, as shown in FIG.31, the electrode fingers 2f and 3f at the uppermost end or having nopatterns adjacent thereto may be thinner than other electrode fingers,or the width of the strip lines of the grating reflector and the MSC maybe smaller than the width of other strip lines.

The photomask has similar problems.

SUMMARY OF THE INVENTION

The present invention is intended to solve the above-described problems,and it is an object of the invention to provide a surface acoustic wavedevice which can prevent improper patterning caused by the proximityeffect.

According to the first invention, there is provided a surface acousticwave device wherein metal patterns provided outside input or outputtransducers on the surface of the substrate for propagating a surfaceacoustic wave along the extension line of the propagation direction ofthe surface acoustic wave have an inclined side with respect to thepropagation direction of the surface acoustic wave.

According to the second invention, there is provided a surface acousticwave device wherein input and output IDTs have electrode fingers whoseroot portions are made wider than other portions where electrode fingersmesh with each other.

There is also provided a surface acoustic wave device wherein theelectrode fingers of input and output IDTs having a much wider spacebetween patterns are made wider than electrode fingers adjacent thereto.

The strip lines of grating reflectors and a multi-strip coupler having amuch wider space between patterns may be made wider than strip linesadjacent thereto.

The width of a portion of the strip line of a multi-strip coupler havinga much wider space between patterns may be made larger than the width ofother portions.

In the surface acoustic wave device according to the first invention,since the surface acoustic wave leaked from the transducer propagateswithout being reflected at the boundaries of the transducer and themetal pattern and is refracted by an impedance gap, it deviates from thepropagation direction of the surface acoustic wave in the transducer. Asa result, most of the wave leaked from both ends of the transducer doesnot return to the inside of the transducer and accordingly, the effectof reflection from end portions of the substrate is small, therebyeliminating deterioration of frequency characteristics.

The surface acoustic wave device according to the second invention canprevent improper patterning by making larger the width of a patternwhich may be thinner or broken by the proximity effect of electronswhich occurs at the time of electron beam exposure.

The above and other objects, features and advantages of the inventionwill become more apparent from the following description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a surface acoustic wave device according toEmbodiment 1 of the present invention;

FIGS. 2(a) and 2(b) is a block diagram of another surface acoustic wavedevice according to Embodiment 1 of the present invention;

FIG. 3 is a block diagram of an exemplary surface acoustic wave deviceof the prior art;

FIG. 4 is a diagram of signal transmission characteristics of the priorart surface acoustic wave device of FIG. 3;

FIG. 5 is a block diagram of another exemplary surface acoustic wavedevice of the prior art;

FIG. 6 is an enlarged view of a passband in the characteristic diagramof the surface acoustic wave device of FIG. 3;

FIG. 7 is an enlarged view of a passband in the characteristic diagramof the surface acoustic wave device of FIG. 5;

FIG. 8 is an enlarged view of a passband in the characteristic diagramof the surface acoustic wave device of FIG. 2(a);

FIG. 9 is a block diagram of a surface acoustic wave device according toEmbodiment 2 of the present invention;

FIG. 10 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 11 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 12 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 13 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 14 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 15 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 16 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 2 of the present invention;

FIG. 17 is a plan view of a surface acoustic wave device according toEmbodiment 3 of the present invention;

FIG. 18 is a plan view of another surface acoustic wave device accordingto Embodiment 3 of the present invention;

FIG. 19 is a plan view of another surface acoustic wave device accordingto Embodiment 3 of the present invention;

FIG. 20 is a plan view of another surface acoustic wave device accordingto Embodiment 3 of the present invention;

FIG. 21 is a plan view of a surface acoustic wave device according toEmbodiment 4 of the present invention;

FIG. 22 is a plan view of another surface acoustic wave device accordingto Embodiment 4 of the present invention;

FIG. 23 is a plan view of a surface acoustic wave device according toEmbodiment 5 of the present invention;

FIG. 24 is a plan view of another surface acoustic wave device accordingto Embodiment 5 of the present invention;

FIG. 25 is a plan view of a surface acoustic wave device according toEmbodiment 6 of the present invention;

FIG. 26 is a plan view of a surface acoustic wave device according toEmbodiment 7 of the present invention;

FIG. 27 is a plan view of a prior art surface acoustic wave device;

FIG. 28 is a plan view of another prior art surface acoustic wavedevice;

FIG. 29 is a plan view of another prior art surface acoustic wavedevice;

FIG. 30 is a plan view illustrating a problem which occurs when anelectron beam is irradiated onto a prior art surface acoustic wavedevice;

FIG. 31 is a plan view illustrating a problem which occurs when anelectron beam is irradiated onto a prior art surface acoustic wavedevice;

FIG. 32 is a block diagram of another surface acoustic wave deviceaccording to Embodiment 1 of the present invention; and

FIG. 33 is a diagram of the configuration of another surface acousticwave device according to Embodiment 1 of the present invention.

Identical reference numerals and labels used in the different drawingfigures refer in each case to the same elements and therefore may not bedescribed in detail for all drawing figures in which such identicalreference numerals or labels are used.

DESCRIPTION OF THE PREFERRED EMBODIMENT Embodiment 1

Preferred embodiments of the first invention will be described hereunderwith reference to FIG. 1 and FIGS. 2(a) and (b).

A surface acoustic wave device according to the preferred embodiment ofthe first invention is structured as shown in FIG. 1 and FIGS. 2(a) and(b) in that two input transducers 2 and one output transducer 3 arearranged alternately along the propagation direction of a surfaceacoustic wave on a piezoelectric substrate 1, the input transducers 2are connected to an input terminal 4 and the output transducer 3 to anoutput terminal 5, and metal patterns 6a and 6b made of a metal thinfilm are formed outside the input transducers 2. The metal thin film isformed by sputtering a metal such as Al, Au and Cu. As shown in FIG.2(a), the metal patterns 6a and 6b are spaced half a wavelength from theinput transducers 2. FIG. 2(b) is a schematic diagram of the phase of anincident wave and a reflected wave.

In this embodiment, the metal patterns 6a and 6b adjacent to the inputtransducers are shaped like a trapezoid compared with the oblong metalpatterns 6 of the prior art shown in FIG. 3. In other words, theabove-described metal patterns 6a and 6b are shaped like a trapezoidhaving a perpendicular side 6x that the surface acoustic wavepropagating from the transducer reaches as a first side and an inclinedside 6y that the surface acoustic wave reaches after it propagatesthrough the location of the metal pattern, these sides being located atthe boundary between the metal pattern and the substrate 1. The angle θof the inclined side 6y is set at a range of more than 5° and less than85°, or more than -85° and less than -5° with respect to the propagationdirection of the surface acoustic wave.

Owing to the above-described structure, in the surface acoustic wavedevice of this embodiment shown in FIG. 1 and FIG. 2(a), the surfaceacoustic wave leaked from the input transducers 2 passes through thetrapezoidal metal patterns 6a and 6b and is reflected and refracted bymismatching of impedance at end portions of the metal patterns 6a and6b. Thereby, the surface acoustic wave which returns to the inputtransducers 2 is slight, and hence, the effect of reflection at endportions of the substrate is extremely small. In this instance, thesides x of the metal patterns 6a and 6b located outside the inputtransducers 2 may be inclined as shown in FIG. 32, or two sides y, y ofthe metal patterns 6a and 6b may be inclined as shown in FIG. 33. Inboth cases, the same effect as described above can be obtained. In FIG.1, reflection which takes place at no-metal small spaces between theinput transducers 2 and the metal patterns 6a and 6b is not taken intoconsideration. However, if it is taken into consideration, the spacesare set at half a wavelength (λo/2) as shown in FIG. 2(a) and FIG. 2(b).Also shown in FIG. 2(b) and labeled as such in each case arerepresentations of (1) a wave which is leaked toward the outside of thestructure, (2) a wave which is reflected by the end portions of theinput transducers 2, and (3) a wave which is reflected by the metalpatterns 6b. Thereby, as shown in FIG. 2(b), the wave reflected by themetal patterns 6a and 6b becomes different from the wave reflected byend portions of the input transducers 2 by a phase of π. Therefore, thewaves are weakened by each other and the effect of reflections from endportions can be further reduced. With the structure shown in FIG. 2(a),frequency characteristics having few ripples as shown in FIG. 8 can beobtained. FIG. 8 shows frequency response characteristic in the passband for the SAW filter of the first embodiment of the presentinvention. This is shown in terms of loss as a function of frequency inthe pass band. As shown on the vertical axis, loss decreases toward zeroin the upward direction. As noted, ripples in the frequencycharacteristics have been substantially decreased.

Embodiment 2

In the above-described embodiment, the metal patterns 6a and 6b locatedoutside the transducers are trapezoidal. They may be pentagonal as shownin FIG. 9, trapezoidal facing opposite directions as shown in FIG. 10,or polygonal with a part of the metal patterns 6a and 6b uncovered withmetal as shown in FIG. 11. As shown in FIG. 12, the metal patterns 6aand 6b may have a waved portion. The embodiment having these patternsproduces the same effect as Embodiment 1.

The above-described metal patterns 6a and 6b are provided between theinput transducers 2 and end portions of the substrate 1 in Embodiment 1,but may be provided to cover the input transducers 2, the outputtransducer 3, the input terminal 4 and the output terminal 5 as shown inFIG. 13, in which metal pattern 6 on substrate 1 covers the entire areaas shown. In this case, the same effect as in Embodiment 1 can beobtained.

In Embodiment 1, the metal patterns 6a and 6b function as floatingelectrodes, but as shown in FIG. 14, both may be grounded. Also, asshown in FIG. 15, the transducers and the metal patterns 6a and 6badjacent thereto may be combined together.

In Embodiment 1, the metal patterns 6a and 6b are located outside thetransducers, but, as shown in FIG. 16, they may be located outside thegrating reflectors 7. In this case, the same effect can be obtained. InFIGS. 14-16, the same reference numerals are used to refer to likeelements which are described in connection with other drawing figuresand a further description of these like elements has therefore beenomitted here.

In each of the above embodiments, a surface acoustic wave deviceconstructed by two input IDTs and one output IDT has been described, buteach of the embodiments can be applied to a surface acoustic wave devicewhich is constructed by a plurality of input IDTs and a plurality ofoutput IDTs. In this case, the same effect can also be obtained.

Embodiment 3

Preferred embodiments of the second invention will be describedhereunder with reference to the accompanying drawings. FIG. 17, FIG. 18,FIG. 19 and FIG. 20 are plan views of different surface acoustic wavedevices. In FIG. 17, FIG. 18, FIG. 19 and FIG. 20, the same componentsas those of FIG. 27 are given the same reference codes and, therefore,their descriptions are omitted.

With reference to FIG. 17, a surface acoustic wave device claimed inclaim 29 will be described hereunder. The comb-like electrode fingers 2aand 2b of the input IDT 2 mesh with each other and the comb-likeelectrode fingers 3a and 3b of the output IDT 3 also mesh with eachother. Main portions 2x and 3x of the electrode fingers which mesh witheach other (2a and 2b, 3a and 3b) and root portions 2y and 3y (whoselengths are equal to the space between the ends 2t and 3t of theelectrode fingers and the other electrodes 2 and 3, respectively) of theelectrode fingers are considered separately.

When patterning of such a surface acoustic wave device as shown in FIG.27 is performed by the electron beam lithography, the root portions ofthe electrode fingers may become thinner than the main portions of theelectrode fingers where electrode finger patterns mesh each other, ormay partially disappear due to the proximity effect of electrons. Toeliminate this problem, the root portions of the electrode fingers aremade wider in advance so that they are prevented from partiallydisappearing even if they thin due to the proximity effect, therebypreventing improper patterning.

FIG. 18 and FIG. 19 show other surface acoustic wave devices which haveroot portions 2y and 3y of the electrode fingers wider than the mainportions and shapes other than that of FIG. 17. The surface acousticwave devices of FIG. 18 and FIG. 19 can produce the same effect as theabove-described embodiment. FIG. 20 shows another surface acoustic wavedevice wherein a root portion of a part of the electrode fingers of FIG.17 is made wider. This surface acoustic wave device can also produce thesame effect as the above-described embodiment. This is because the linewidth of the root portions of the electrode fingers having few linepatterns in the proximity thereof easily becomes smaller in the electronbeam lithography. In the case of the surface acoustic wave device shownin FIG. 17, the root portions which are apt to thin are on the left endof the input IDT 2 and the right end of the output IDT 3.

Embodiment 4

FIG. 21 and FIG. 22 are plan views of surface acoustic wave devices ofthe present invention claimed in claim 30. In FIG. 21 and FIG. 22, thesame components as those of FIG. 27 are given the same reference codes,and accordingly, their descriptions are omitted.

When patterning of such a surface acoustic wave device as shown in FIG.27 is performed by the electron beam lithography, electrode fingershaving a much wider space between patterns may become thinner than otherelectrode fingers due to the proximity effect of electrons. To eliminatethis problem, electrode fingers having a much wider space betweenpatterns are made wider in advance so that this phenomenon caused by theproximity effect can be prevented.

In FIG. 21, electrode fingers having a much wider space between patternsare 2c and 3c of the uppermost end patterns of the surface acoustic wavedevice, which have few patterns in the proximity thereof. In FIG. 22,electrode fingers having a much wider space between patterns are 2c and3c of the uppermost end patterns of the surface acoustic wave device and2d and 3d facing the space between the input IDT and the output IDT.

As an example of the above-described embodiment, a surface acoustic wavedevice constructed only by the input IDT and the output IDT has beendescribed, but the embodiment can be applied to a surface acoustic wavedevice provided with, for example, grating reflectors in addition tothese IDTs, and the same effect can be obtained.

Embodiment 5

FIG. 23 and FIG. 24 are plan views of surface acoustic wave devices ofthe present invention claimed in claim 31. In FIG. 23 and FIG. 24, thesame components as those of FIG. 28 are given the same reference codes,and accordingly, their descriptions are omitted.

When patterning of such a surface acoustic wave device as shown in FIG.28 is performed by the electron beam lithography, the strip line of thegrating reflector having a much wider space between patterns may becomethinner than other strip lines due to the proximity effect of electrons.To eliminate this problem, the strip line having a much wider spacebetween patterns is made wider in advance so that this phenomenon causedby the proximity effect can be prevented.

In FIG. 23, the strip line having a much wider space between patternsfrom among the strip lines constituting the grating reflector 7 is 7a ofthe uppermost end pattern of the surface acoustic wave device, which hasfew patterns in the proximity thereof. In FIG. 24, in which the samereference numerals are used to designate like elements as used in FIG.23, the strip lines having a much wider space between patterns are 7a ofthe uppermost end pattern of the surface acoustic wave device and 7bfacing the IDT.

As an example of the above-described embodiment, a surface acoustic wavedevice constructed only by input and output IDTs and grating reflectorshas been described, but the embodiment can be applied to a surfaceacoustic wave device provided with, for example, a multi-strip couplerin addition to these IDTs and grating reflectors, and the same effectcan be obtained.

Embodiment 6

FIG. 25 is a plan view of a surface acoustic wave device of the presentinvention claimed in claim 32. In FIG. 25, the same components as thoseof FIG. 29 are given the same reference codes, and accordingly, theirdescriptions are omitted.

When patterning of such a surface acoustic wave device as shown in FIG.29 is performed by the electron beam lithography, the strip line of themulti-strip coupler having a much wider space between patterns maybecome thinner than other strip lines due to the proximity effect ofelectrons. To eliminate this problem, the strip line having a much widerspace between patterns is made wider in advance so that this phenomenoncaused by the proximity effect can be prevented.

In FIG. 25, the strip line having a much wider space between patterns is8a of the uppermost end patterns of the multi-strip coupler, which hasfew patterns in the proximity thereof.

Embodiment 7

FIG. 26 is a plan view of a surface acoustic wave device of the presentinvention claimed in claim 33. In FIG. 26, the same components as thoseof FIG. 29 are given the same reference codes, and accordingly, theirdescriptions are omitted.

When patterning of such a surface acoustic wave device as shown in FIG.29 is performed by the electron beam lithography, a portion of the stripline of the multi-strip coupler having a much wider space betweenpatterns may become thinner than other portions due to the proximityeffect of electrons. To eliminate this problem, the portion of the stripline having a much wider space between patterns is made wider in advanceso that this phenomenon caused by the proximity effect can be prevented.

In FIG. 26, the portion of the strip line of the multi-strip couplerhaving a much wider space between patterns is 8w of the strip line 8a atboth ends of the multi-strip coupler. 8w is the portion which has noadjacent patterns constituting input and output transducers.

In each of the above embodiments, the patterning of a surface acousticwave device has been described, but each of the above embodiments can beapplied to the patterning of a photomask used in the surface acousticwave device as described in the foregoing. In this case, the same effectas the above-described embodiments can be obtained. The space betweenpatterns is preset in the stage of design layout.

In each of the above embodiments, a surface acoustic wave deviceconstructed by one input IDT and one output IDT has been described, buteach of the embodiments can be applied to a surface acoustic wave devicewhich is constructed by a plurality of input IDTs and a plurality ofoutput IDTs. In this case, the same effect can also be obtained.

As described on the foregoing pages, according to the first invention,since the metal patterns located outside the transducers are formed suchthat the surface acoustic wave is scattered, the surface acoustic wavedevice can be produced with ease at a low cost and does not deterioratefrequency characteristics even if it is made small in size.

As described on the foregoing pages, according to the second invention,improper patterning at the time of electron beam exposure can beprevented by making root portions of the electrode fingers wider thanother portions without changing the conventional production process,whereby stable production of a surface acoustic wave device is possible.

Moreover, the electrode fingers and the strip line of the gratingreflector and the multi-strip coupler having a much wider space betweenpatterns are made wider than other electrode fingers and other striplines, respectively, to prevent the pattern width from becoming thinnerat the time of electron beam exposure, without changing the conventionalproduction process, whereby stable production of a surface acoustic wavedevice is possible.

Furthermore, a portion of the strip line of the multi-strip couplerhaving a much wider space between patterns is made wider than otherportions of the strip line to prevent the strip line from partiallythinning at the time of electron beam exposure, without changing theconventional production process, whereby stable production of a surfaceacoustic wave device is possible.

What is claimed is:
 1. A surface acoustic wave device comprising asubstrate for propagating a surface acoustic wave, and input and outputtransducers formed on the surface of said substrate with each having twoopposite electrodes each of which has a plurality of electrode fingerpatterns extending toward their opposites and meshing with the electrodefinger patterns of their opposites, wherein at least some of saidelectrode finger patterns of said transducers are more widely spacedapart from adjacent patterns than the other electrode finger patterns ofsaid transducers, characterized in thatthose electrode finger patternsof said transducers which are more widely spaced apart from adjacentpatterns and thus tend to become thinner when later exposed to electronbeam lithography, are made wider than the other electrode fingerpatterns of said transducers.
 2. The surface acoustic wave deviceaccording to claim 1 wherein said electrode finger patterns which aremade wider are located at the outermost ends of said input and outputtransducers.